Chromosome 16 inversion, inv(16), is one of the most common chromosome abnormalities in human acute myeloid leukemia (AML). A fusion gene between the core binding factor B (CBFB) gene and the myosin heavy chain 11 (MYH11) gene is generated by this inversion. CBFB encodes a transcription factor while MYH11 encodes the smooth muscle form of myosin heavy chain (SMMHC). To identify target genes of CBFb-SMMHC that are important in leukemia, we are taking two separate approaches: 1. serial analysis of gene expression (SAGE) of human leukemia samples and 2. cDNA microarray analysis of mouse embryonic stem (ES) cells with CBFB-MYH11 expression. Using SAGE, we performed genome-wide analyses of gene expression in 5 AML cases with inv(16). One SAGE library was made from each patient sample and over 50,000 tags were sequenced from each library. The results were analyzed relative to SAGE data from a normal bone marrow library. For the cDNA microarray analysis, RNA from mouse ES cells with CBFB-MYH11 turned on or off was isolated and used to generate cDNA probes to hybridize to a mouse 31K array. Potential target genes are now confirmed by quantitative PCR and promoter regions are being analyzed. These two complementary approaches will hopefully facilitate the identification of true targets of CBFB-MYH11 during leukemogenesis. Using a yeast two-hybrid screening approach we identified the c-Myc promoter binding protein (MBP-1) as a binding target of CBFB. MBP-1 binds to the promoter of the c-Myc gene and negatively regulate the expression of c-Myc, which is dysregulated in most cancer cells including leukemia, resulting in unbalanced control of cell proliferation, differentiation, or apoptosis. Subsequent studies suggest that MBP-1 may be a functional bridge between c-Myc and CBFB-MYH11 in human leukemia. We have generated mice expressing CBFB-MYH11 with various deletions of MYH11 by gene targeting in mouse ES cells. These mice are analyzed for defects in blood formation and in leukemia development. This study will tell us the functional domains of MYH11 required for leukemia development.